Digestive System Anatomy

• Digestive tract– Alimentary tract or

canal– GI tract

• Accessory organs– Primarily glands

• Regions– Mouth or oral cavity– Pharynx– Esophagus– Stomach– Small intestine– Large intestine– Anus

Digestive Tract Histology

Digestive System Regulation

• Nervous regulation– Involves enteric nervous

system• Types of neurons:

sensory, motor, interneurons

– Coordinates peristalsis and regulates local reflexes

• Chemical regulation– Production of hormones

• Gastrin, secretin

– Production of paracrine chemicals• Histamine • Help local reflexes in ENS

control digestive environments as pH levels

Peritoneum and Mesenteries

• Peritoneum– Visceral: Covers organs– Parietal: Covers interior

surface of body wall– Retroperitoneal: Behind

peritoneum as kidneys, pancreas, duodenum

• Mesenteries– Routes which vessels and

nerves pass from body wall to organs

– Greater omentum– Lesser omentum

Oral Cavity• Mouth or oral cavity

– Vestibule: Space between lips or cheeks and alveolar processes

– Oral cavity proper• Lips (labia) and

cheeks• Palate: Oral cavity

roof– Hard and soft

• Palatine tonsils• Tongue: Involved in

speech, taste, mastication, swallowing

Teeth

• Two sets– Primary, deciduous,

milk: Childhood– Permanent or

secondary: Adult (32)

• Types– Incisors, canine,

premolar and molars

Tooth structure:

Salivary Glands• Produce saliva– Prevents bacterial

infection– Lubrication– Contains salivary

amylase• Breaks down starch

• Three pairs– Parotid: Largest– Submandibular– Sublingual: Smallest

Pharynx and Esophagus

• Pharynx– Nasopharynx– Oropharynx: Transmits

food normally– Laryngopharynx:

Transmits food normally

• Esophagus– Transports food from

pharynx to stomach– Passes through

esophageal hiatus (opening) of diaphragm and ends at stomach• Hiatal hernia

– Sphincters• Upper• Lower

Deglutition (Swallowing)

• Three phases– Voluntary• Bolus of food moved by tongue from oral cavity to

pharynx– Pharyngeal

Reflex: Upper esophageal sphincter relaxes, elevated pharynx opens the esophagus, food pushed into esophagus

– Esophageal• Reflex: Epiglottis is tipped posteriorly, larynx

elevated to prevent food from passing into larynx

Phases of Deglutition (Swallowing)

Functions• IngestionIngestion: Introduction of food into stomach• MasticationMastication: Chewing• PropulsionPropulsion– Deglutition: Swallowing– Peristalsis: Moves material through digestive tract

Stomach Anatomy:

• Openings– Gastroesophageal

: To esophagus– Pyloric: To

duodenum

• Regions– Cardiac– Fundus– Body– Pyloric

Stomach Histology:• Layers– Serosa or visceral

peritoneum: Outermost

– Muscularis: Three layers• Outer longitudinal• Middle circular• Inner oblique

– Submucosa– Mucosa

Stomach Histology• Rugae: Folds in

stomach when empty• Gastric pits: Openings

for gastric glands– Contain cells

• Surface mucous: Mucus• Mucous neck: Mucus • Parietal: Hydrochloric

acid and intrinsic factor • Chief: Pepsinogen • Endocrine: Regulatory

hormones

Hydrochloric Acid Production

Phases of Gastric Secretion

Movements in Stomach

Small Intestine• Site of greatest amount of

digestion and absorption• Divisions

– Duodenum– Jejunum– Ileum: Peyer’s patches or

lymph nodules• Modifications

– Circular folds or plicae circulares, villi, lacteal, microvilli

• Cells of mucosa– Absorptive, goblet, granular,

endocrine

Movement in small intestine:

• Mixing: Segmental contraction that occurs in small intestine• Secretion: Lubricate, liquefy, digest• Digestion: Mechanical and chemical• Absorption: Movement from tract into circulation or lymph• Elimination: Waste products removed from body

Small Intestine Secretions

• Mucus – Protects against digestive enzymes and stomach acids

• Digestive enzymes– Disaccharidases: Break down disaccharides to

monosaccharides– Peptidases: Hydrolyze peptide bonds– Nucleases: Break down nucleic acids

• Duodenal glands – Stimulated by vagus nerve, secretin, chemical or tactile

irritation of duodenal mucosa

Duodenum and Pancreas

Duodenum Anatomy and Histology

Liver• Lobes– Major: Left and right– Minor: Caudate and

quadrate

• Ducts– Common hepatic– Cystic

• From gallbladder

– Common bile• Joins pancreatic duct at

hepatopancreatic ampulla

Blood and Bile Flow

Duct System

Gallbladder

• Bile is stored and concentrated• Stimulated by cholecystokinin and vagal

stimulation• Dumps into small intestine• Production of gallstones possible– Drastic dieting with rapid weight loss

Pancreas

• Anatomy– Endocrine

• Pancreatic islets produce insulin and glucagon

– Exocrine• Acini produce digestive

enzymes

– Regions: Head, body, tail

• Secretions– Pancreatic juice

(exocrine)• Trypsin• Chymotrypsin• Carboxypeptidase• Pancreatic amylase• Pancreatic lipases• Enzymes that reduce DNA

and ribonucleic acid

Bicarbonate Ion Production

Gastric hormones:

Figure 24.20a, b

Liver Histology

portal triad

3. Architecture of the Hepatic Parenchyma

The hepatic lobule is the structural unit of the liver.

Central vein

Portal vein

Bile duct

Sinusoids

Liver cells (Hepatocytes)Hepatic arteryPortal area

Bile

• Bile acid• Phospholipids• Cholesterol• Bilirubin• Waste products• Electrolytes• Mucin

…each day around 600 ml of bile is produced…

Functions of the Liver• Bile production

– Salts emulsify fats, contain pigments as bilirubin• Storage

– Glycogen, fat, vitamins, copper and iron; huge blood reservoir of blood (storage); very high lymph flow

• Nutrient interconversion – Metabolic functions (see next slide)

• Detoxification– Hepatocytes remove ammonia and convert to urea; metabolizes drugs,

hormones; has the Cytochrome P-450 enzyme system.• Phagocytosis – Cleans the blood

– Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria

• Synthesis– Albumins, fibrinogen, globulins, heparin, clotting factors

Liver’s Role in Metabolism

Carbohydrate Metabolism• Storage of large amounts of glycogen• Conversion of galactose and fructose to glucose• Gluconeogenesis• Formation of many chemical compounds from intermediate

products of carbohydrate metabolism

Fat Metabolism• Beta-oxidation of fatty acids to supply energy to for other

functions in the body• Synthesis of cholesterol, phospholipids, and most lipoproteins

(and their receptors)• Synthesis of fats from proteins and carbohydrates

Liver’s Role in Metabolism (cont’d)

Protein Metabolism• Deamination of amino acids• Formation of urea for removal of ammonia from the body

fluids• Formation of plasma proteins• Interconversion of the various amino acids and synthesis of

other compounds from amino acids

Exocrine Pancreas – Enzymes

• Trypsinogen• Chymotrysinogen• Carboxypeptidases• Pro-elastase• Phospholipase• pancreatic lipase• Pancreatic amylase

Bicarbonate Ion Production

Lipoproteins

• Types– Chylomicrons

• Enter lymph

– VLDL– LDL

• Transports cholesterol to cells

– HDL• Transports cholesterol

from cells to liver

Water and Ions:

• Water– Can move in either direction

across wall of small intestine depending on osmotic gradients

• Ions– Sodium, potassium, calcium,

magnesium, phosphate are actively transported

Large Intestine:

• Extends from ileocecal junction to anus• Consists of cecum, colon, rectum, anal canal• Movements sluggish (18-24 hours)

Large Intestine

• Cecum– Blind sac, vermiform appendix attached

• Colon– Ascending, transverse, descending, sigmoid

• Rectum– Straight muscular tube

• Anal canal– Internal anal sphincter (smooth muscle) – External anal sphincter (skeletal muscle) – Hemorrhoids: Vein enlargement or inflammation

Secretions of Large Intestine

• Mucus provides protection– Parasympathetic stimulation increases rate of

goblet cell secretion

• Pumps– Exchange of bicarbonate ions for chloride ions– Exchange of sodium ions for hydrogen ions

• Bacterial actions produce gases called flatus

Histology of Large Intestine

Movement in Large Intestine

• Mass movements– Common after meals

• Local reflexes in enteric plexus– Gastrocolic: Initiated by stomach– Duodenocolic: Initiated by duodenum

• Defecation reflex– Distension of the rectal wall by feces

• Defecation– Usually accompanied by voluntary movements to expel feces

through abdominal cavity pressure caused by inspiration

Reflexes in Colon and

Rectum:

Digestion, Absorption, Transport

• Digestion – Breakdown of food molecules for absorption into

circulation • Mechanical: Breaks large food particles to small• Chemical: Breaking of covalent bonds by digestive

enzymes

• Absorption and transport– Molecules are moved out of digestive tract and

into circulation for distribution throughout body

Effects of Aging

• Death of myenteric plexus neurons• Atrophy of sphincter muscles

Incontinence• Decrease in mucus layer, connective tissue, muscles and

secretions• Increased susceptibility to infections and toxic agents– Ulcerations and cancers